The new triisocyanates are particularly suitable for use as isocyanate components in low solvent, two-component polyurethane lacquers which are lightfast. Low solvent or solvent-free, lightfast two-component polyurethane lacquers of this kind have been described, for example, in German Auslegeschrift No. 2,304,893, British Pat. No. 1,402,658 or U.S. application Ser. No. 616,108 filed on Sept. 23, 1975. The lacquer systems described there have considerable advantages compared with the prior art systems described in the same document. However, the polyisocyanates with an isocyanate functionality greater than 2 which are described as particularly suitable in this prior publication still have high viscosities, being in the region of about 1000 to 2500 cP/20.degree. C., so that it is essential to use relatively large quantities of reactive diluents in the lacquer systems according to German Auslegeschrift No. 2,304,893 in order to obtain sufficiently low viscosities for spraying. The cycloaliphatic diisocyanates also mentioned in German Auslegeschrift No. 2,304,893 are of only limited usefulness in this field of application because of their lower isocyanate functionality and doubtful physiological properties.
It was, therefore, an object of the present invention to provide new polyisocyanates which would contain aliphatic isocyanate groups and have an isocyanate functionality greater than 2 and a viscosity below about 200 cP/20.degree. C. Furthermore, the new isocyanates should preferably have isocyanate groups attached to primary carbon atoms so that they would be sufficiently reactive with compounds containing isocyanate-reactive groups. The new isocyanates should also have a low vapor pressure and be practically odorless at room temperature.
This problem was substantially solved by preparing the new triisocyanates described below. These new triisocyanates are particularly valuable starting materials for the production of polyurethane resins, in particular as isocyanate components in two-component polyurethane lacquers.